Over in another thread
has posited the idea of re-dressing the Matrix in a D&D-esque fantasy setting.
Here I will lay out the basics, in my vision of this thought experiment:
* Deep in the underworld, Illithids (mindflayers) gather the living (but paralyzed or unconscious) bodies of humanoid slaves or captives, and place them in a form of sleep/suspended animation.
* The youngest Illithid larva feed off the dreams of these "dreamers" for sustenance.
* Once the larvae have matured sufficiently, they are gradually inserted into the brains of the "dreamers", forming, over time, a symbiotic bond. (Eventually the mind of the "dreamer" will be entirely subsumed, and a mature Mindflayer will arise, the original host effectively dead. However, for our purposes, let us assume this process takes a significant period of time.)
* To keep the "dreamers" docile and to keep them from waking up, the Illithids have manufactured or accessed a "dream world", where the unwitting "dreamers" think they live. In reality, of course, the dreamers lie in vats or pods in a series of caverns deep underground.
* The Dream is a fairly normal fantasy life, but the Illithids sometimes insert themselves into this world to look for problems or intruders. They travel the dream realm as Paladins
: impossibly handsome, yet emotionless knights who patrol the kingdom of the Dream world as agents of the "King" and hunt down any anomalies.
* Much like Agents in the Matrix, these Paladins can modify the Dream when necessary, but must limit doing so lest they create a dissonance and more of the dreamers 'reject' the Dream world.
(Perhaps this is how this all started:)
* However, there is some way to wrest oneself from the Dream. Or, perhaps, someone has made their way into one of these Breeding Places where the dreamers lie, and broken someone out of there. Either way, there are now a handful of "survivors" who have emerged from the Dream into the Real World and now find themselves trying to survive in the underworld environment.
* (It could also be entirely plausible to posit that, for some magical reasons
, some dreamers must be allowed to escape, lest they poison the Dream itself, or because of some special rules of the Dream World.)
* The Real World environment is a serious of caverns deep underground. The Illithids keep a great number of monstrous creatures down here, and, when necessary, control them psionically to defend themselves from intruders or invaders. Generally, however, the monsters simply wander around looking for food. (There is a possibility that the survivors, if they could distract the Illithids, or protect a particular monster from psionic control, might manage to use some of these monsters to their advantage, although generally they must do their best to avoid them... otherwise, it's "kill or be killed" down here.)
* The survivors know of a method for extracting others from the Dream world, but it requires entering it yourself and contacting the person inside the false reality.
* Once that is done, the person needs to be located in the real world and rescued. If they have already been "seeded" with an Illithid larva, things become more complex:
a) At some point, the larva will kill the host and subsume its personality.
b) A powerful alchemical substance may be manufactured, which, if injected into the brain of the host body, forces the larva out. However, this is difficult, expensive, or takes a long time.
c) If the formula is not on hand, the survivor will have to be "rescued" with the parasite still in their brain, and is an effective time bomb (or worse), until the process can be carried out.
(Option C gives us the potential for lots of interesting Mafia-like interactions between the survivors, if desired.)
* Potentially, we could use different game rules for the Dream world (something fit for high fantasy, or a simplified ruleset, and which allows unusual magical powers or some other form of reality-bending) and the real world (which uses a gritty and deadly dungeon crawling ruleset).
As the game progresses, the community of escapees must survive, finding safe places, food, weapons, and earning experience and skills. If things go well, they community grows (by rescuing more people from the Illithid vats) and eventually escapes or overthrows the Illithid masters (a possible endgame).
However, if they are discovered or killed, the game has been lost.
Otherwise, the game is fairly standard "dungeon crawl" and would run very well in your typical D&D-esque ruleset (I'd go totally old school for this, myself), with the exception that the PCs have no safe place to retreat to except what they can establish for themselves.
Each player controls a 'stable' of characters and decides which to send on various delves or missions. If they are killed, you write up a new community member as your character.
The size of the community and number of people acts as a form of "hit points" for the group; run out of characters to play and you've lost the game.
Therefore, the players will have to raid the Dream vats on a regular basis to recruit new members (and thereby replenish or grow their numbers).